Cells can be stably transduced with a number of viral vectors including retroviruses and adeno-associated viruses. Retrovirus-based vectors are useful due to their ability to transduce cells efficiently with target nucleic acids, and because of their ability to integrate a target nucleic acid into a cellular genome.
Adeno-associated viral ("AAV") vectors are also used to transduce cells with target nucleic acids, e.g., those which inhibit deleterious gene function. AAV is replication defective, requiring co-infection with a helper virus such as adenovirus for productive infection. However, AAV vectors efficiently transduce many different cell types, including hematopoietic cells. Cells transduced with AAV vectors do not have to be actively dividing as in the case of retroviral vectors.
AAV vectors have no endogenous promoter activity, permitting expression of desired recombinant sequences within the AAV vector from engineered promoters. AAV vectors are used to inhibit, e.g., viral infection, by including anti-viral transcription cassettes in the AAV vector. For example, Chatterjee et al. (Science (1992), 258: 1485-1488, hereinafter Chatterjee et al. 1) describe anti-sense inhibition of HIV-1 infectivity in target cells using an AAV vector with a constitutive expression cassette expressing anti-TAR RNA. Chatterjee et al. (PCT application PCT/US91/03440 (1991), hereinafter Chatterjee et al. 2) describe AAV vectors, including AAV-vectors which express antisense TAR sequences. Chatterjee and Wong (Methods, A companion to Methods in Enzymology (1993), 5: 51-59) further describe AAV vectors for the delivery of antisense RNA.
AAV vectors have several properties which make them preferred gene delivery systems. They have no known mode of pathogenesis and 80% of people in the United States are currently seropositive for AAV. Because AAV vectors have no endogenous promoter activity, specific promoters may be used, depending on target cell type. Packaged AAV vectors can be concentrated so that multiplicities of infection exceeding 1.0 can be used in transduction experiments. This allows virtually 100% of the targets in a culture to be transduced, obviating the need for selection of transduced cells.
This invention provides composite viral vectors with elements for host chromosome integration derived from one virus and a replication-defective rescuable viral genome which includes an anti-viral agent derived from another virus. The anti-viral agent is generally directed against the virus corresponding to the replication-defective portion of the vector. Cells transduced by this construct block infection by wild-type versions of the replication-defective virus. Moreover, if the infecting virus successfully replicates within the transduced cell, the replication-defective portion of the vector (including the anti-viral agent) will also replicate, causing the anti-viral activity contained within the replication-defective construct to spread throughout an infected host, in parallel with the viral infection. Thus, the construct provides protection against infection by a particular virus, and the protection is amplified upon infection by the virus.